Television broadcast signals, both terrestrial and cable system transmission, have been provided in accordance with various standards. For example, the National Television System Committee (NTSC), phase alternating line (PAL), and sequential color with memory (SECAM) analog broadcast color standards have been utilized in different regions of the world for a number of years. Various broadcast systems (e.g., systems B, D, G, H, I, K, L, M, and N), defining channel layout and modulation techniques, have been used throughout the world. The use of these varied broadcast standards has presented challenges for the makers of transmission and receiver equipment. For example, different tuner and filter configurations have been traditionally required for use with a particular broadcast standard, such as in set-top boxes, television sets, etc.
The recent deployment of digital television, such as using the Advanced Television Systems Committee (ATSC), digital video broadcasting-terrestrial (DVB-T), International Telecommunication Union (ITU) j.83, integrated services digital broadcasting-terrestrial (ISDB-T), and digital terrestrial multimedia broadcast (DTMB) digital broadcast standards, has added to the foregoing challenges. In particular, it is a challenge for manufacturers to support both an existing analog broadcast standard as well as a digital broadcast standard, much less support all such broadcast standards.
A typical television implementation for receiving signals of both an analog and digital broadcast standard is shown in FIG. 1 as receiver 100. Receiver 100 includes multi-conversion tuner 110, such as generally would comprise a double conversion low intermediate frequency (IF) tuner configuration, providing frequency conversion of broadcast signals (whether terrestrial, cable, etc.) to a selected low IF. Multi-conversion tuner 110 is typically configured to provide a high level of image rejection, such as through the use of image reject mixers, additional filters, etc., in order to mitigate images appearing within the desired band in association with the use of the IF.
Two separate signal processing paths are included in receiver 100 to processing of analog broadcast signals and digital broadcast signals. The processing path for analog signals includes channel filter 120 (typically a surface acoustic wave (SAW) filter) which is centered at the low IF and provides a precise pass-band for allowing substantially only a single channel of the relevant analog broadcast standard to pass. Analog demodulator 130 is provided to demodulate the analog broadcast signal and provide a composite video baseband signal (CVBS) and sound IF. The processing path for digital signals includes channel filter 140 (typically a SAW filter) which is centered at the low IF and provides a precise pass-band for allowing substantially only a single channel of the relevant digital broadcast standard to pass. Digital demodulator 150 is provided to demodulate the digital broadcast signal and provide a digital video signal and sound IF. It should be appreciated that a same channel filter may not be shared between the signal processing path for analog signals and the signal processing path for digital signals due to differing design requirements, such as to deal with vestigial sidebands etc.
The foregoing configuration provides a relatively complex tuner configuration in which a series of tuners provide frequency conversion. Moreover, images associated with the use of the multi-conversion tuner configuration demand a high level of image rejection be provided with this tuner configuration. The filtering requirements of the channel filters in the foregoing configuration demand the cutoff characteristics of SAW filter implementations. Thus it can be appreciated that the receiver configuration is not well suited to a high level of integration or simplification.
In order to accommodate multiple analog broadcast standards and/or multiple digital broadcast standards, and thus provide a flexible receiver solution, the receiver configuration would require a plurality of filters 120 and/or a plurality of filters 140. For example, to accommodate multiple analog broadcast standards a separate filter 120, adapted for use with a particular one of the analog broadcast standards, would need to be provided for each such broadcast standard. Similarly, to accommodate multiple digital broadcast standards a separate filter 140, adapted for use with a particular one of the digital broadcast standards, would need to be provided for each such broadcast standard. These filters and their attendant selection circuitry provide a receiver configuration even less suited to a high level of integration that illustrated in FIG. 1.
Past efforts to create a flexible receiver solution have resulted in unsatisfying architectures which sacrifice performance for lower cost and reduced power consumption. Performance issues such as dynamic range and channel cross modulation are symptoms of low power operation combined with inadequate architecture. Moreover, such solutions have required large blocks of software code to be uploaded to the tuner before operation with a given broadcast standard, thus providing undesirable deployment and initialization issues.